Heat Stroke and Hyperthermia in Dogs

Increased Body Temperature and Heat Stroke in Dogs

Hyperthermia is an elevation in body temperature that is above the generally accepted normal range. Although normal values for dogs vary slightly, it usually is accepted that body temperatures above 103° F (39° C) are abnormal.

Heat stroke, meanwhile, is a form of non-fever hyperthermia that occurs when heat-dissipating mechanisms of the body cannot accommodate excessive external heat. Typically associated with temperature of of 106° F (41° C) or higher without signs of inflammation, a heat stroke can lead to multiple organ dysfunction.

This condition can lead to multiple organ dysfunction. Temperatures are suggestive of non-fever hyperthermia. Another type, malignant hyperthermia, is an uncommon familial non-fever hyperthermia that can occur secondary to some anesthetic agents.

Hyperthermia can be categorized as either fever or non-fever hyperthermias. Fever hyperthermia results from inflammation in the body (such as the type that occurs secondary to a bacterial infection). Non-fever hyperthermia results from all other causes of increased body temperature.

Other causes of non-fever hyperthermia include excessive exercise, excessive levels of thyroid hormones in the body, and lesions in the hypothalamus, the part of the brain that regulates body temperature.

Non-fever hyperthermia occurs most commonly in dogs (as opposed to cats). It can affect any breed, but is more frequent in long-haired dogs and short-nosed, flat-faced dogs, also known as brachycephalic breeds. It can occur at any age but tends to affect young dogs more than old dogs.

Symptoms and Types

Hyperthermia can be categorized as either fever or non-fever hyperthermias; heat stroke is a common form of the latter. Symptoms of both types include:

Causes

Excessive environmental heat and humidity (may be due to weather conditions, such as a hot day, or to being enclosed in an unventilated room, car, or grooming dryer cage)

Upper airway disease that inhibits breathing; the upper airway (also known as the upper respiratory tract) includes the nose, nasal passages, throat (pharynx), and windpipe (trachea)

Underlying disease that increases likelihood of developing hyperthermia, such as paralysis of the voice box or larynx; heart and/or blood vessel disease; nervous system and/or muscular disease; previous history of heat-related disease

Poisoning; some poisonous compounds, such as strychnine and slug and snail bait, can lead to seizures, which can cause an abnormal increase in body temperature

Anesthesia complications

Excessive exercise

Risk Factors

Previous history of heat-related disease

Age extremes (very young, very old)

Heat intolerance due to poor acclimatization to the environment (such as a heavy coated dog in a hot geographical location)

Obesity

Poor heart/lung conditioning

Underlying heart/lung disease

Increased levels of thyroid hormone (hyperthyroidism)

Short-nosed, flat-faced (brachycephalic) breeds

Thick hair coat

Dehydration, insufficient water intake, restricted access to water

Treatment

Early recognition of the symptoms of heat stroke is key to a prompt recovery. If your dog's increased body temperature can be linked to environmental temperature, such as weather, an enclosed room, grooming cage or exercise, the first immediate step will be to attempt to lower the body temperature.

It is very important to avoid ice or very cold water, as this may cause blood vessels near the surface of the body to constrict and may decrease heat dissipation. A shivering response also is undesirable, as it creates internal heat. Lowering the temperature too quickly can lead to other health problems, a gradual lowering is best. The same guideline applies to drinking water. Allow your dog to drink cool, not cold, water freely. However, do not force your dog to drink.

You will need to have your dog examined by a veterinarian to ensure that a normal temperature has been reach and has stabilized, and that no long lasting damage has taken place within the organs or brain. Complications, such as a blood-clotting disorder, kidney failure, or fluid build-up in the brain will need to be immediately and thoroughly treated. Your doctor will check your dog's blood clotting times, and kidney function will be analyzed in part by urinalysis. An electrocardiogram may also be used to observe your dog's heart capabilities and any irregularities that might have resulted as a result of the hyperthermic condition.

In many cases patients need to be hospitalized until their temperature is stabilized, and may even need intensive care for several days if organ failure has occurred. Oxygen supplementation via mask, cage, or nasal catheter may be used for severe breathing problems, or a surgical opening into the windpipe or trachea may be required if upper airway obstruction is an underlying cause or a contributing factor. Intravenous feeding or a special diet may need to be prescribed until your dog's organs have recovered to handle a normal diet again.

Underlying disease conditions or factors that increase the likelihood of developing hyperthermia will also need to be corrected and treated if possible (e.g., obesity, heart/lung disease, grooming with respect to environmental temperatures, restricting activity with respect to age).

Prevention

Dogs that have suffered an episode of hyperthermia are prone to experiencing it again. Be aware of the clinical signs of heat stroke so you may respond quickly to an episode. Know how to cool your dog properly, and talk to your veterinarian about the appropriate procedures for maintaining proper body temperature and lowering it in the safest way possible.

If your dog is older, or is a brachycephalic breed that is prone to overheating, avoid taking your dog out during the hottest times of day, or leaving the dog in places that can become too hot for your dog, like a garage, sunny room, sunny yard, or car. Never leave your dog in a parked car, even for only a few minutes, as a closed car becomes dangerously hot very rapidly. Always have water accessible to your dog; on hot days you might even add ice blocks for your dog to lick.

If you have not done so already, you may wish to invest in a pet CPR class. It can mean the difference between your dog living or dying should an episode of heat stroke occur.

spraying

The act of urinating on objects or areas as a method of marking territory

pharynx

A cavity in the mouth where the respiratory systems and gastrointestinal systems come together

larynx

The voice box; this is one part of the respiratory system

systemic

Something that is related to the whole body and not just one particular part or organ

malignant

Something that becomes worse or life threatening as it spreads

tachypnea

The term for a quick heartbeat

urinalysis

An in-depth examination of the properties of urine; used to determine the presence or absence of illness

upper respiratory tract

The section of the respiratory system that contains the mouth, nose, pharynx, larynx, trachea, and epiglottis.

trachea

The windpipe; it carries air from the bronchi to the mouth

hypothalamus

Part of the thalamus that helps to regulate the release of certain hormones

hyperthermia

High body temperature

ataxia

A medical condition in which an animal is unable to control the movements of their muscles; may result in collapse or stumbling.

anesthetic

Any substance known to eliminate feeling; usually applied during a painful medical procedure.

acute

Term used to imply that a situation or condition is more severe than usual; also used to refer to a disease having run a short course or come on suddenly.

brachycephalic

An animal with a wide head, short in stature.

electrocardiogram

A record of the activity of the myocardium

hematemesis

The act of throwing up blood

groin

The area between the abdomen and thighs; the inguinal area

gait

The term used to describe the movement of an animal

acclimatization

The act of helping an animal to adjust to something or some place foreign to them.